Systems and methods for calculating call blocking for alternate call routing schemes

ABSTRACT

Systems and methods are provided wherein call-blocking probability of a telecommunications system is calculated based on consideration of over flow paths and alternate routes. Once the routes and overflow pathways are identified, the total number of call attempts and calls failed, due to congestion, is determined from statistical route data. Dividing the number of failed calls due to congestion by the number of attempted calls results in the blocking proportion for each route that is used by the methods disclosed herein to calculate the probability of blocking for that route.

CROSS REFERENCE TO PROVISIONAL APPLICATION

This patent claims benefit of U.S. Provisional Application Nos.60/408,055, filed Sep. 4, 2002, entitled “Blocking Calculation Processfor Alternate Routing Schemes,” and 60/488,106, filed Jul. 17, 2003,entitled “Arithmetic Routing Analysis Method.” Each provisional patentapplication is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to new and improved systems and methods forproviding calculations for determining blocking probability foralternate call routing in a telecommunications system.

2. Description of Related Art

Today's telecommunications systems have become large and easily reachmost places in the world. Almost every home in the United States has itsown telephone line, which is connected to a local switch in the nearesttown or county, from there to a main switch in the nearest city, andfrom there to any other city in any other country in the world. Theseswitches, or exchanges, as they are sometimes called, are interconnectedthrough wires or lines, known as trunks. In this way, a person is ableto dial another party in another country just was easily as if they weredialing someone on the same street.

For large and complicated networks to work properly, mathematics andcomputer simulation are used to understand and simulate the network. Theaim is to design and control large networks to provide reliablecommunications systems and to use the network resources efficiently. Thereliable and efficient operation of networks is of vital commercialimportance to both users and telecommunications companies. Even modestpercentage improvements in network efficiency can correspond toincreases in quality for users and large revenue gains fortelecommunications companies.

A large network may be affected by many factors, which are often hard topredict. There typically are busy and quiet periods throughout the day,sometimes expected and sometimes unexpected. For example, if atelevision program has a phone-in vote, there can be a sudden overloadat one point or increment of time on the network. If a transmission lineis lost due to a sudden or unexpected failure, the network can becomeoverloaded if an adequate alternate call routing scheme was not inplace.

Mathematicians have developed ways of calculating call routing schemesto route calls that can cope with these unpredictable events. Thesealternate call routing schemes typically operate by searching for sparecapacity in a deterministic way in the network so as to route calls awayfrom parts of the network that overloaded or temporarily off-line andinto parts that can better handle the additional capacity or overflow.

Call blocking for call routing schemes is a key performance indicator(KPI) for the core of a telecommunications network. Unfortunately, theuse of alternate routing schemes, complex IMT meshes and the inabilityto cause redirection due to distant trunk congestion makes thecalculation of this key performance indicator extremely difficult. Thepurpose of this invention is to provide a new and useful method thatuses probability theory to accurately estimate the probability of callblocking in a network with alternate routing capability.

SUMMARY OF THE INVENTION

As outlined above, conventional systems have not recognized or provideda system for calculating call blocking probability for a communicationssystem that considers all possible alternate routes in the resultingblocking probability. Accordingly, it is an object of the presentinvention to provide a system and method for providing a call blockingprobability-calculating method that accurately estimates the probabilityof call blocking in a network with alternate routing capability.

This invention provides method for calculating the probability of a callbeing blocked in a network having a plurality of routes by determiningat least a first and second probability (B_(p)) of a call being blockedon the primary and secondary route, wherein a second incoming callenters the network at the secondary route and the second probabilityconsiders the impact of the second call. From this series ofdetermination steps the first probability and the second probability aresummed to provide an overall probability of blocking for the call overprimary routes and alternate routes.

This invention further provides a method for determining the number ofcalls blocked in the network according to an expression in which thenumber of incoming calls at the primary route and the number of incomingcalls at the secondary route are considered.

This invention also provides a method for calculating the probability ofa call being blocked in a network having a plurality of routes forming aroute set, wherein the number of legs in each route and the probabilityof blocking for each leg are determined and calculating the blocking inthe network based on the determining steps.

This invention separately provides a method for rerouting calls from oneroute to another based on the probability of blocking for the availableroutes.

In various exemplary embodiments according to this invention, theprobability of blocking for switch-to-switch, route-set, and MSC-PSTNegress are calculated.

These and other features and advantages of this invention are describedin or apparent from the following detailed description of theapparatus/systems and method according to this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of this invention will be described indetail, wherein like reference numerals refer to identical or similarcomponents or steps, with reference to the following figures, wherein:

FIG. 1 illustrates an exemplary block diagram of a communicationsnetwork having an alternate routing scheme according to this invention;

FIG. 2 illustrates an exemplary block diagram of an alternate routingcase according to an embodiment of this invention;

FIG. 3 illustrates an exemplary routing scheme having multiple legsaccording to this invention;

FIG. 4 illustrates an exemplary three route alternate routing schemeaccording to this invention; and

FIG. 5 illustrates an exemplary embodiment of a call routing scheme withIMT overflow according to this invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The exemplary embodiments of the systems and methods according to thisinvention provide a method for performing call blocking probabilitycalculations in a telecommunications network.

A blocked call results when a call cannot be connected. The two mostcommon reasons for blocked calls are: 1) all lines or trunks to or fromthe central office or exchange are in use or otherwise unavailable or 2)all paths to or from a PABX (Private Automatic Branch Exchange) orswitch are in use or unavailable. Thus, based on these examples it maybe necessary for a telecommunication network to calculate an alternaterouting scheme to connect the call.

In these embodiments, alternate routing is defined as the process ofredirecting a call over alternate routes when the primary route for thatcall is unavailable. That primary route, referred to as the P0 route,will overflow to one or more alternate routes comprised of secondary andtertiary high-usage trunk groups. These secondary and tertiaryhigh-usage trunk groups are referred to as P1, P2, P3 and so on untilall the routes in an alternate routing scheme are labeled in the orderin which they are selected. A route is any path that connects at leasttwo switching centers (nodes).

The expression for the probability of blocking can be found for analternate routing scheme by first determining the routes that comprisethe scheme and the overflow paths. Once the routes and overflow pathwaysare identified, the total number of call attempts and calls failed dueto congestion can be determined from statistical route data. Dividingthe number of failed calls due to congestion by the number of attemptedcalls results in the blocking proportion for each route that is used bythe methods disclosed herein to calculate the probability of blockingfor that route. The blocking expressions for switch-to-switch,route-set, and MSC-PSTN egress are described below.

FIG. 1 illustrates a communications network 100 wherein routing nodes1-8 interconnect a network of mobile stations and nodes. The nodes 1-8represent switches, with the lines between the nodes representingtrunks. Also illustrated are a sending (or calling) mobile station 10and a receiving mobile station 20. In this illustration, the remainingmobile stations have not been labeled. It should be appreciated that anyof the mobile stations shown in FIG. 1 can be sending or receivingmobile stations.

Prior to connecting a call from mobile station 10 to mobile station 20,a routing scheme is calculated to determine the optimal routing sequenceusing any number of nodes 1-8 to route call data from the sending mobilestation 10 to the receiving mobile station 20. The primary routingscheme (P0), as discussed above, represents the best probability ofconnecting the call based on a blocking probability. The blockingprobability is conventionally a percentage-based estimate of thesuccessful connection of a call through each of the nodes 1-8. At entrynode 1, a value is calculated based on the number of other incomingcalls, the number of calls currently connected and the resourcesavailable at entry node 1. For example, entry node 1 may have an 80%probability of routing success. According, to the illustration in FIG.1, from entry node 1 a call may be routable to any of secondary nodes 5,6 or 8. Each of secondary nodes 2,3 and 5-8 has a similar probability ofrouting success associated with it. Depending on the percentages at eachof these secondary nodes 2,3 and 5-8, it may be more optimal to nextroute the call to secondary node 7 for final completion to destinationnode 4, which is connected to the receiving mobile station 20.

Based on a combination of those percentages, a routing case iscalculated for the call from mobile station 10 to mobile station 20.Included in the routing case a primary routing scheme (P0) iscalculated. Also calculated are secondary and tertiary (P1, P2, P3,etc.) routing schemes for the call. Should for some reason the primaryrouting scheme (P0) fail the secondary and tertiary routing schemes areused as back up to connect the call.

Switch-to-Switch Calculations

In an alternate routing scheme (called a routing case in Ericssonterminology) where the routes are statically defined, the probability ofunsuccessfully delivering a call from one node to another due tocongestion is simply the product of the individual blockingprobabilities for all nodes (entry, secondary and destination) in theselected route. The destination nodes are those nodes that connect theswitch to the receiving mobile station 20, in FIG. 1 the destinationnode is shown as node 4.

An illustrative block diagram of a routing case is shown in FIG. 2,wherein X, Y and Z represent the offered calls and B_(p), B_(j), andB_(f) representing the blocking proportion for the primary (P0),secondary (P1), and tertiary (P2) routing schemes, respectively.

FIG. 2 illustrates a routing case 200 for a telecommunications systemaccording to the embodiments of this invention. The routing case 200consists of three routing schemes that include a primary route (P0) 210,a secondary route 220 (P1) and a tertiary route 230 (P2). It should beappreciated that routes can be defined depending on the number ofavailable routes. For illustrative purposes, only three routes have beendefined, i.e., primary (P0), secondary (P1) and tertiary (P2).

As shown in FIG. 2 and in operation of the communications network, thecall attempts to access the primary route 210 first (Incoming Calls X)then overflows to the secondary route 220 and finally to the tertiaryroute 230. The method disclosed by this example, perceives a blockedcall due to route congestion only when the call fails to gain access tothe tertiary route 230. In addition to incoming calls X, there are alsoincoming calls Y and Z which are offered to the secondary and tertiaryroutes 220 and 230, respectively as their first choice. The secondaryroute 220 is then the primary route for incoming calls Y and thetertiary route 220 is the primary route for incoming calls Z, leading toa system of call traffic comprised of three traffic inputs: X, Y, and Z.

The systems and methods according to this invention are used to derivethe blocking probability by setting the number of call attempts equal toX and solving for the number of successful and failed calls with respectto X. The blocking proportion B_(p) for the primary route 210 (P0) isP0=B _(p)=Blocks_(p)/Attempts_(p)

wherein

-   -   Blocks_(p)=number of blocks of the primary route and    -   Attempts_(p)=total number of call attempts for the primary route

The number of overflowed calls from the primary route is equal toXB_(p). The overflowed calls combine with the incoming calls (IncomingCalls Y) to the secondary route 220 to create the offered call traffic[XB_(p)+Y] to the secondary route 220. The number of calls that overflowfrom the secondary route 220 to the tertiary route 230 is (XB_(p)+Y)B_(j). The overflowed calls from the secondary route 220 combine withthe incoming calls to the tertiary route 230 (Incoming Calls Z) tocreate the offered call traffic [Z+(XB_(p)+Y)B_(j)] to the tertiaryroute 230. The total number of customer perceived blocked calls for theentire communications network is (Z+(XB_(p)+Y)B_(j))B_(f).

To calculate the blocking probability with respect to X, the terms ofthe blocked calls formula X, Y and Z are grouped, the Y and Z are set tozero, and the number of blocked calls are divided by X. The result isB_(p)B_(j)B_(f) and represents the probability of a customer perceivedblocked call for all calls that attempted the primary route 210 first(Incoming Calls X). Use the same procedure to calculate the blockingprobabilities for the Y and Z components by setting either X and Z or Xand Y to zero. The results are B_(j)B_(f) and B_(f), respectively. Thismanual process forms the backbone for all calculations involvingswitch-to-switch blocking analysis, according to this invention.

In the exemplary embodiments of this invention, if the probability ofblocking for the primary and secondary routes 210 and 230 is 1 (100%blocking), the blocking rate for the routing case 200 simplifies toB_(f), which is the blocking proportion for the tertiary route 230.Substituting the tertiary route 230 blocking proportion for the routingcase blocking rate represents an easy way to calculate the worst caseblocking for a routing case. However, when the blocking proportions forthe primary and secondary routes 210 and 230 are included in thecalculation, the routing case 200 blocking rate will decrease as theblocking proportions for those routes drop below 1.

It should be appreciated that the number of components in the blockingprobability analysis increases as the number of routes in the routingcase increase. Since the blocking proportion must be less than or equalto 1.0 for any route, the routing case blocking probability will almostalways decrease as additional routes are added to the routing case.

Route-Set Blocking

Referring to FIG. 3, in many cases, the call path from an entry node tothe destination node is comprised of multiple legs, such as passingthrough one or more switches (secondary nodes) via IMT (inter-machinetrunk) prior to reaching the destination node. In this case, the jointprobability of the combination of the legs must be used to calculate theblocking probability for that routing scheme. For example, if asecondary route for a routing scheme is an IMT to another MSC (mobileswitching center) followed by another secondary route to the destinationnode, then both secondary routes must be successful at the same time forthe call to succeed.

The Arithmetic Routing Analysis Method is used once again to derive theblocking probability expression for routing schemes with multiple legsby setting the number of call attempts equal to X and solving for thenumber of successful and failed calls with respect to X. In FIG. 3, arouting scheme is shown comprising a first leg 310 and a second leg 320,the blocking proportion for the first leg 310 is given as B_(L1);therefore, the number of attempts that successfully seize a channel onthe route is X(1−B_(L1)) while the number of blocked calls is X(B_(L1)).Thus, X(1−B_(L1)) calls will arrive at the second switch for an attempton the second leg 320 of the route set. The probability of failure forthe second leg 320 is X(1−B_(L1))(B_(L2)). The total number of failedcalls due to blocking for this route set is equal to the first leg 310failures [X(B_(L1))] plus the second leg 320 failures[(1−B_(L1))(B_(L2))] and is expressed as X(B_(L1))+X(1−B_(L1))(B_(L2)).The probability of blocking is found by dividing the number of blockedcalls by the number of attempts. This is equal toB_(L1)+(1−B_(L1))(B_(L2)). Expanding the equation yieldsB_(L1)+B_(L2)−B_(L1)B_(L2) which is equal to the joint probability offailure for the two (first and second) routes in the routing scheme.

If the first leg 310 (P0 _(L1)) and second leg 320 (P0 _(L2)) in theabove example are engineered to 1.0% blocking each, then the overallblocking for the routing scheme would be 0.01+0.01−0.01*0.01 which isequal to 1.98%. The blocking probability for a routing scheme willalmost always increase as additional routes are added to the routingscheme.

If the first leg 310 (PO_(L1)) is engineered to 0.0% GoS and the secondroute (PO_(L2)) engineered to 1.0% blocking, then the overall blockingfor the routing scheme would be 0+0.01−0*0.01 which is equal to 1%. Whenthe blocking proportion for an IMT route is 0, the IMT blockingproportion component can be eliminated from a routing scheme blockingcalculation.

Entry Node to Destination Node Blocking

Since most wireless networks use a combination of IMTs and direct trunksfor outbound PSTN connectivity, switch-to-switch and routing schemeblocking calculations are required to identify the expressions forMSC-to-PSTN egress (Entry Node to Destination Node) blocking. Inaddition, since most communication networks do not use route redirectionfor distant trunk congestion, ARAM must be performed manually as it wasin FIG. 3.

The Laws of ARAM

-   -   1) For switch-to-switch calculations, the blocking proportion        corresponding to the tertiary route is almost always greater        than the actual customer perceived blocking.    -   2) For a route-set, the blocking probability will almost always        increase as additional routes are added to the route-set.    -   3) For a route-set, when the blocking proportion for a first        route is 0, the blocking proportion component can be eliminated        from the routing scheme blocking calculation.

Using the methods of ARAM, in addition to customer perceived PSTNblocking, it is possible to calculate blocking for mobile-to-mobilecalls via IMT, mobile-to-land calls that traverse a transit switch,mobile subscriber (MS) access to the MSC, and other types of traffic.

There are three steps for switch and market calculations using ARAM.These steps are:

1. Routing Case Identification (Route Discovery)

2. Data Collection

3. Post Processing

-   -   a. Routing Case Calculations    -   b. MSC Calculations    -   c. Group Calculations        Routing Case Identification (Route Discovery)

Before the customer perceived blocking can be calculated, two criticalelements must be defined and identified: 1) the routes (including theirnodes) that comprise the secondary and tertiary routing schemes and 2)each node's corresponding busy hours must be identified. Once theseitems have been defined and identified, using the methods discussedherein one can collect and post-process the data, yielding the blockingcalculations for the MSC(s), communication market(s) and coverageregion(s).

A necessary aspect of the customer perceived blocking is identificationof the routes that comprise the alternate routing schemes because theyform the basis of all calculations. This route discovery process shouldbe performed for each MSC or component of the routing case.

For each routing case, all possible route choices within the routingscheme are identified and sequentially labeled as P0, P1, P2, etc. withP0 representing the primary route, P1 representing the secondary route,and so on until the final or last resort route is reached. Ifswitch-to-PSTN egress calculations are required, all routing schemesincluding the individual routes belonging to the routing case areidentified and sequentially labeled.

Described below are a series of examples that illustrate the methodsused to identify routes within a routing scheme.

Example 1 Simple 3 Route Alternate Route Scheme (Switch-to-Switch)

The example shown in FIG. 4 is a simple case in which there are threeroutes in a routing case 400 used to connect a call from the sendingmobile station 460 to the receiving mobile station 450. The primaryroute P0 is a type 2B route to an end office 420. The secondary route P1is a type 2A route to an access tandem 430. The tertiary route P2 is anIXC route to the IXC carrier 440.

The routes should be itemized in the order in which they are selectedincluding the selection number (i.e. P0, P1, etc.), the route name, andthe route type.

In the example shown in FIG. 4, the blocking probability for the routingcase 400 is:=P0*P1*P2

Example 2 Simple Alternate Route Scheme with IMT Overflow(Switch-to-Egress)

If one of the routes is an IMT route, then the possible choice of routesfor the connecting MSC must be included in the route list since theycontribute to the success and failure of the call. In the example shownin FIG. 5, the primary route P0 is a type 2A route to an access tandem530. The secondary route P1, and in this case the final route for theMSC 510, is an IMT route to MSC 520. This IMT route is labeled P1 _(L1)since it is the first leg in the route set, or hop, for the P1 route.Once the call arrives via the P1 _(L1) IMT to MSC 520, there are tworoute choices. The first is a type 2A route to the same access tandem530. This route is referred to as the P1 _(L2A) route since it is thefirst choice route for the second leg of the P1 route. If this route iscongested, then the second choice route is an IXC route to the IXC 540,referred to as the P1 _(L2B) route since it is the second choice routefor the second leg of the P1 route set.

In this exemplary embodiment, the blocking probability for the P1 routeis calculated by taking the joint probability of the IMT route blockingand the overall blocking rate for the two alternate routes for MSC 520.Combining the blocking probability for the P1 route set with theblocking rate for the primary route P0 results in the overall blockingfor this scheme. This can be expressed as:

$\begin{matrix}{= {{P0}*{P1}}} \\{= {{P0}*\left\lbrack {{P1}_{L1} + {P1}_{L2} - \left( {{P1}_{L1}*{P2}_{L2}} \right)} \right\rbrack}} \\{= {{P0}*\left\lbrack {{P1}_{L1} + \left( {{P1}_{L2A}*{P1}_{L2B}} \right) - \left( {{P1}_{L1}*{P1}_{L2A}*{P1}_{L2B}} \right)} \right\rbrack}}\end{matrix}$

If the blocking rate for the P1 _(L1) IMT is 0.0%, then the equationsimplifies to=P0*P1_(L2A) *P1_(L2B)

If the blocking rate for the P1 _(L1) IMT is 100.0%, then the equationsimplifies to=P0Data Collection

One exemplary method that can be used to calculate the blockingprobability for a routing scheme using routing cases is to use therouting case blocking probabilities that correspond to the routing casebusy hours in the calculation. This means that for each routing case,the blocking probabilities could have been measured at different times.The result is the average individual routing case busy hour (IRCBH)blocking for the routing schemes which provide the average worst caseblocking for those schemes. This sampling method is equivalent to anICBH (individual cell busy hour) RF blocking calculation.

A second exemplary method that can be used to measure the alternateroute blocking for a routing scheme is to sum the routing case attemptson an hourly basis and then set the system busy hour to the time inwhich the largest number of attempts occurred. This provides theindividual MSC system busy hour (IMSBH) and can be used to calculate theblocking probability during the system (switch) busy hour. If the sum ofthe routing case attempts is not available, another indicator such asthe entry node busy hour can be used to identify the IMSBH.

Once the routing schemes have been identified and the routes thatcomprise those schemes listed are in order of selection, one mustidentify the top monthly busy hours for each routing case or for eachMSC in the area of question, depending on the type of calculationperformed (average IRCBH or average IMSBH). The number of busy hoursused may vary, but the recommendation is a value between 10 and 15 permonth used consistently for each switch. Once the busy hours have beenidentified, the route data corresponding to these busy hours iscollected and averaged. The route data should include the following:

-   -   the number of attempts    -   the number of blocks    -   the number of defined circuits for each route

Once the route data has been collected and averaged, the data can bepost processed and used to determine the routing case blockingprobabilities, switch blocking probabilities, market blockingprobabilities, and so forth.

Post Processing

There are three types of calculations that can be made in the postprocessing process, depending on the type of information desired.

-   -   1) Routing Case Blocking    -   2) MSC Blocking    -   3) Group Blocking

To calculate the routing case blocking probabilities, the individualroute blocking proportions are used to calculate either theswitch-to-switch (node-to-node) or switch-to-PSTN egress (secondarynode-to-destination node) routing case blocking probabilities. Forreference, the individual route blocking proportion should be found withthe following equation:P _(x) =B _(x)=Blocks_(x)/Attempts_(x)

The routing case blocking probability expressions must be defined inorder to calculate the routing case blocking probability. If they havenot, please refer to the Overview and Process Definition section of thisdocument for a description on how to do this.

To calculate the overall customer perceived PSTN blocking for a MSC(regardless of the blocking calculation type), perform a weightedaverage of all the routing case blocking probabilities using the averagenumber of attempts for each routing case as the weight. The closed formexpression for the MSC blocking rate (i.e. blocking of routing caseswithin a switch) is:

$\frac{\sum\limits_{{rc} = 1}^{L}\;\left( {P_{rc}*{ATT}_{rc}} \right)}{\sum\limits_{{rc} = 1}^{L}\;{ATT}_{rc}}$

wherein

-   -   L=number of routing cases for switch    -   P_(rc)=blocking probability for routing case rc    -   ATT_(rc)=avg # of attempts for routing case rc

The equation shown above can provide both the individual routing casebusy hour (IRCBH) blocking and the individual MSC system busy hour(IMSBH) blocking. Either the average IRCBH blocking or the IMSBHblocking can represent the PSTN blocking rate for the MSC. The averageIRCBH blocking should always be equal to or greater than the IMSBHblocking.

To calculate the overall blocking for a group of switches, such as amarket and/or region containing a group of MSCs, the equation can bemodified to perform a weighted average of either the average IRCBH orIMSBH for each MSC using the sum of the average number of routing caseattempts for each MSC as the weight (or some other traffic dependentweight), as shown in the following equation. The resulting calculationwill provide either the average switch-to-switch or averageswitch-to-PSTN egress blocking probability.

$\frac{\sum\limits_{{msc} = 1}^{K}\;\left( {P_{msc}*{ATT}_{msc}} \right)}{\sum\limits_{{msc} = 1}^{K}\;{ATT}_{msc}}$

wherein

-   -   K=number of MSCs for the market or region    -   P_(msc)=blocking probability for switch MSC    -   ATT_(msc)=total avg. number attempts for switch MSC

While this invention has been described in conjunction with theexemplary embodiments outlined above, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the exemplary embodiments of theinvention, as set forth above are intended to be illustrative, notlimiting. Various changes may be made without departing from the spiritand the scope of the invention.

1. A method for calculating the probability of a call being blocked in anetwork having a plurality of routes, comprising: measuring a firstprobability (B_(p)) of a call being blocked on the primary route;measuring a second probability (B_(d)) of a call being blocked at thesecondary route, wherein a second incoming call enters the network atthe secondary route and the second probability considers the impact ofthe second call; summing the first probability and the secondprobability; and determining the number of calls blocked in the networkaccording to the expression B_(d)(XB_(p)+Y) in which X represents thenumber of incoming calls at the primary route and Y represents thenumber of incoming calls at the secondary route.
 2. A method forcalculating the probability of a call being blocked in a network havinga plurality of routes forming a route set, comprising: determining thenumber of legs in each route; determining the blocking probability foreach leg; and calculating the blocking in the network according to theequation:${1 - {\prod\limits_{z = 1}^{M}\;\left( {1 - P_{z}} \right)}},$ whereinM is the number of legs for the route and P_(z) is the blockingprobability for leg z.
 3. The method of claim 2 wherein the network hasthe ability to reroute calls from one route to another and wherein thecalculating step is performed according to the equation:${\prod\limits_{y = 1}^{N}\;\left\lbrack {1 - {\prod\limits_{z = 1}^{M}\;\left( {1 - P_{yz}} \right)}} \right\rbrack},$wherein N is the number of routes in routing case, M is the number oflegs for each route y in routing case and P_(yz) blocking probabilityfor route y on leg z.
 4. A method for calculating the probability of acall being blocked in a network having a plurality of routes forming aroute set wherein the network is capable of rerouting network trafficbased on the probability of blocking, comprising: measuring a firstprobability (B_(p)) of a call being blocked on the primary route;measuring additional probabilities of a call being blocked on each ofthe remainder of the routes in the route set, wherein additionalincoming calls may enter the network on the remainder of the routes andthe additional probabilities considers the impact of the additionalincoming calls; and calculating the probability of the route setblocking according to the equation:${\prod\limits_{y = 1}^{N}\;\left\lbrack {1 - {\prod\limits_{z = 1}^{M}\;\left( {1 - P_{yz}} \right)}} \right\rbrack},$wherein N is the number of routes in routing case, M is the number oflegs for each route y in routing case and P_(yz) blocking probabilityfor route y on leg z.